"Amor maternus" means, indeed, "maternal love" or "love belonging to a mother", "love of a mother", or "mother's love".It could mean "love for a mother" in just the way that, in English, "love of a mother" could mean "love for a mother" ("love of money" or "love of beer"). Same for "amor matris" in Latin, unfortunately. (Allen & Greenough on genitive §342: petitio consulatûs = candidacy for the consulship, regnum civitatis = power over the state).Both "amor matris" and "amor maternus" more mean "mother's love" than "love for a mother". Normally, in the other sense, you can say "amor pro matre" for 'love for a mother" or "amor matri". ["metus/amor hostilis (dative)" = "fear of the enemy"/"love of the enemy" = "fear for/love for"]

The specific chapter in my grammar book covers the use of the genitivus subjectivus and objectivus with the use of substantiva verbalia (and in which cases you shouldn't use them). The second example was in another part of the book.